Many of today's conventional complementary metal-oxide-silicon (CMOS) field effect transistor (FET) operational amplifiers obtain the needed high gain by using two stages, with each stage comprising a pair of load devices, a differential pair of devices and a current source, or by using a single stage amplifier having a pair of load devices, two separate pairs of cascode devices, a differential pair of devices and a current source. These types of amplifiers typically require large compensation capacitors which result in a greater settling time and more noise than is desired in some applications. Another problem with these types of amplifiers is that variations in the magnitude of the power supply voltages used cause a loss of operating margins which cannot be easily tolerated in some applications.
It is desirable to have a CMOS operational transconductance amplifier which has relatively high gain, has relatively low noise, has relatively good power supply rejection, has moderate output impedance, and has relatively short settling time.